The invention is based on a multi-beam radar sensor having at least one transmitter/receiver element on a substrate and having a focusing body, which is assigned to each transmitter/receiver element for prefocusing, as generically defined by the preamble to the main claim. Radar sensors in which common antennas are used for both transmission and reception, so-called monostatic radar sensors, are known for instance from International Patent Disclosure WO 97/02496. In this case, an FMCW radar sensor for a vehicle is proposed for detecting objects; in it, three transmitter/receiver elements, for instance, or transmission/reception antenna feeds, or so-called patches, are mounted on the lateral structure of a microstrip. In the beam path, before each patch, there is additionally a dielectric aerial, to achieve better illumination of the dielectric lens and thus to attain prefocusing. However, it has been found that proper function of the dielectric aerial is assured only if the dielectric aerial is positioned exactly. Even the slightest deviation from the ideal position causes overshadowing of the lens or coupling to adjacent dielectric aerials.
From German Patent Disclosure DE 197 10 811 A1, a further device for aimed projection and/or pickup of electromagnetic waves is known. This device comprises at least one antenna element, one dielectric lens, and one dielectric body, which is disposed between the antenna element and the dielectric lens. This dielectric body again serves to prevent overshadowing of the dielectric lens and serves to prefocus the electromagnetic millimeter waves projected or picked up by the antenna element. To simplify the exact adjustment required, the dielectric body is stretched out flat and is preferably cup-shaped. It is considered unfavorable in this respect that the electromagnetic waves of the individual antenna elements are not decoupled by the dielectric body, since one common dielectric body is used for all the antenna elements.